1. Field of the Invention
The invention relates to a substrate lift for semiconductor substrates. More particularly, the invention relates to a substrate lift that can simultaneously support multiple substrates in a single cell.
2. Description of the Background Art
Semiconductor substrates or wafers are processed to produce integrated circuits using a series of processes. Each of these processes are performed in a distinct type of process cell. Other cells, known as metrology cells, are used to measure substrates. An assemblage of cells served by at least one substrate transport robot is known as a cluster tool. The substrate transfer robot resides in a transfer cell that is typically connected to each of the plurality of process cells such that the robot can access a semiconductor substrate positioned in each one of the process cells, and the robot can transfer the substrate between the various cells.
Some substrate transfer robots are configured to contain one robot blade that can handle one substrate at a time. Other substrate transfer robots have two back-to-back robot arms attached to a single robot hub. Each robot arm supports a distinct robot blade. Robot blades, known alternatively as end effectors, are those portions of the robot that support the substrate (from above, below, or other relative attitudes). In the back-to-back robot arm configuration, when a first end effector is moved in a process cell to interact with a substrate, the second end effector is constrained to be oriented 180 degrees away from the first end effector. When the second end effector is constrained in a position as a result of the first substrate interacting with a substrate, the second end effector is typically not positioned to perform any useful process or transfer on any substrate. The second end effector is thus limited to holding a substrate (or not holding any substrate) until the first end effector completes a substrate transfer.
Each cell is typically configured to hold one substrate at a time. If a second substrate is inserted into a cell that contains a first substrate, the second substrate, or the end effector supporting the second substrate, would collide with or interfere with the first substrate. Swapping the substrates in a cell thus requires a robot to remove the first substrate from the cell before the second substrate is inserted into the cell. As the first substrate is removed from the cell to permit insertion of the second substrate into the cell, the first substrate is temporarily stored somewhere remote from the process cell, and the second substrate to permit the robot end effector to be used to insert the second substrate into the cell. The above described substrate swapping not only necessitates challenging robot motion, but provides a bottleneck for substrate processing that reduces substrate throughput.
Therefore, a need exists in the art for an apparatus or method that increases throughput by increasing the number of substrates that can be simultaneously held within a cell so the substrates can be swapped. A need also exists for a single robot that can swap a substrate to be inserted into a cell with a substrate already in the cell.
An apparatus and associated method transporting a first substrate and a second substrate relative to a cell. The cell contains a pedestal that is configured to interact with a single substrate when swapping substrates, a first substrate is displaced from the pedestal to a remote location using a two substrate lift device and a second substrate is inserted into the cell and onto the pedestal. The present invention is especially applicable in cells in which substrates are displaced using a robot, and may be used in a variety of process cells and metrology cells.